Israel hit more than 20 “targets” inside Gaza after it killed the head of the Islamist organisation's military wing, Ahmed Said Khalil al-Jabari, along with another Hamas official, in a missile strike against the car in which they were traveling.

Al-Jabari has “a lot of blood on his hands,” said Israeli military spokeswoman Lt Col. Avital Leibovitch, while a statement from the Ezzedine al-Qassam Brigades warned: “The occupation has opened the gates of hell on itself,” vowing the militants would "continue the path of resistance”.

It was part of a wider Israeli operation against militant groups in the Hamas-run Gaza Strip, the Israel Defence Force said, and followed a wave of rocket attacks against Israel.

There were scenes of chaos at Shifa Hospital in Gaza City, as dozens of seriously injured patient were stretchered in, ambulances tearing off to collect more casualties.

Gaza’s health ministry said 10 civilians have been killed, including two young children – an 11-month-old and a six-year-old – while at least 45 people were wounded, 10 of them in critical condition.

A spokesperson for the IDF confirmed on Twitter that the Israeli Navy was attacking Gaza from the sea, saying: “All options are on the table. If necessary, the IDF is ready to initiate a ground operation in Gaza.”

“We recommend that no Hamas operatives, whether low level or senior leaders, show their faces above ground in the days ahead,” the spokesperson tweeted.

Thirteen rockets fired from Gaza into southern Israel had been intercepted by the country’s missile defence system, the spokesperson said, tweeting with the #PillarofDefense.

Member of the PLO executive committee and chief Palestinian negotiator Saeb Erekat condemned the assassinations.  “We condemn in the strongest terms this new Israeli assassination which aims to initiate a bloody escalation. We hold the Israeli government fully responsible for the consequences that this new act of aggression would bring to the region.”

“This exposes that Israel has an agenda for war but not for peace.”

In a press conference held overnight, Defence Minister Ehud Barak said Israel was not interested in engaging in war but Hamas’s provocation over the last few days had forced Israel to act.

One Gaza resident, a doctor, posted this on her Facebook page as the Israeli bombardment continued: “Gaza is under extensive Israeli military attack … the hospitals are already lacking essential emergency medications, and citizens were called for blood donation, we do not have power … we expect more escalation.”

The Egyptian foreign minister, Mohamed Kamel Amr, condemned the attacks and called on Israel to stop the strikes immediately, warning any further escalation from Israel "could have negative repercussions on the security and stability of the region".

The video of al-Jabari’s assassination was posted on YouTube by the Israeli Defence Force. Just 14 seconds long, it is shot from the air, following a car along an urban street before a missile strike all but obliterates the sedan.

Jaabari is the most senior Hamas operative to be killed by Israel for almost four years, since Operation Cast Lead, its three-week assault on Gaza, left around 1,400 Palestinians dead.

He was widely believed to have been intimately involved in the Hamas takeover of Gaza in 2007, and played a key role in overseeing the imprisonment of Israeli soldier Gilad Shalit, who was snatched by Palestinian militants while on a patrol near the Gaza Strip in 2006 and held in secret locations in Gaza until his release in October 2011, in return for the release of 1027 Palestinian prisoners.

In a rare public appearance, Jaabari personally escorted Shalit to the Rafah Crossing with Egypt as part of the prisoner exchange.

Israel's air strikes have prompted anger, fear and panic in Gaza, with residents anticipating a prolongued Israeli military campaign, some buying up bread and other essentials while others crowding outside the coastal strip’s hospital and morgues to hold a vigil for the injured and mourn the dead.

Meanwhile the Muslim Brotherhood’s Freedom and Justice Party issued its own condemnation."Israel's return to the policy of assignation of leaders from the Palestinian struggle groups shows that the Israeli occupation wants to drag the region towards instability.”

Meanwhile the Muslim Brotherhood’s Freedom and Justice Party issued its own condemnation."Israel's return to the policy of assignation of leaders from the Palestinian struggle groups shows that the Israeli occupation wants to drag the region towards instability.”